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Frame Rate Conversion Reference

Compare ways to convert footage between frame rates like 24, 30, 60, and 120 fps. Use it to understand when clips will play slower, repeat frames, blend motion, or need optical flow for smoother slow motion.

Why this tool is useful

Frame rate conversion goes wrong quietly. A clip conformed from 25 to 23.976 plays at the wrong speed with pitched audio. Footage converted with frame blending looks soft on motion in a way nobody notices until the grade. A 24 fps sequence pulled down to 29.97 develops a cadence judder that reads as a compression problem. In each case the timeline appears correct on a still frame.

This reference shows what actually happens to the frames for each conversion method. Pick a source and target rate and it lays out conforming, 3:2 pulldown, frame sampling, blending, and optical flow side by side, with the resulting runtime change, audio pitch shift, and frame-level cadence for each, so you can choose the method deliberately instead of accepting whatever your NLE defaults to.

Source frame rate

Target frame rate

Conversion method

Conform / Interpret Footage

This method does not create new frames. It takes the original source frames and plays them faster at the target frame rate, so the motion stays clean because every frame is real, but the clip becomes shorter and any synced audio would need attention.

Source frames

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Output timeline

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Original frame

Frame conversion visualizer

This uses one generated shot, a ball bouncing and settling, then resamples it from the selected source FPS to the selected target FPS. Toggle the conversion method, play the preview, and use the frame strip to inspect the output frames.

Original output frame
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Output frame 124 preserved source frames

Example use cases

  • Mixing PAL and NTSC sources

    Decide how 25 fps archive material should join a 23.976 timeline, and whether the runtime and pitch change from conforming is acceptable.

  • Planning slow motion

    Check what a 120 fps clip does on a 23.976 timeline, and when optical flow is worth the render time against a straight conform.

  • Preparing a broadcast deliverable

    Work out the cadence implications of taking a 23.976 master to 29.97 for broadcast before the file goes to technical QC.

FAQ

Conforming reinterprets the existing frames at a new rate without creating or discarding any. Every original frame survives intact, but the clip changes duration and any embedded audio shifts in pitch. Converting keeps the duration the same and changes the frames instead, by duplicating, dropping, blending, or synthesising them. Conforming is the right choice when picture integrity matters more than runtime, such as 24 to 23.976. Converting is necessary when the runtime is fixed, such as delivering to a broadcast slot.
Use optical flow when you need genuinely smooth motion and the material suits it: clear subject movement, consistent lighting, no heavy motion blur, and nothing crossing in front of anything else. It estimates motion between real frames and generates new intermediate images, which looks far better than blending when it works. It fails visibly on fast pans, transparency, water, particles, fine repeating detail, and overlapping subjects, producing warping and tearing artefacts. Frame blending is the safer fallback: softer on motion, but it degrades predictably instead of breaking. Always review optical flow output at full resolution before committing to it.
A 3:2 pulldown distributes 24 fps material into a 29.97 fps stream by alternating between spreading one source frame across three fields and the next across two. It exists to fit film-rate material into the NTSC broadcast cadence without changing runtime. You need it for legacy NTSC broadcast delivery, and you need to remove it when bringing telecined material back for editing, because working with an unremoved pulldown gives you a mixed cadence that makes clean cuts and speed changes difficult. Modern progressive delivery paths mostly avoid it.
It comes from the introduction of colour to NTSC television. Adding the colour subcarrier to the existing black-and-white signal required slowing the frame rate by a factor of 1000/1001, which turned 30 fps into 29.97 and, by extension, 24 into 23.976. The 0.1 percent offset is small enough to be invisible in playback and large enough to cause real synchronisation drift over a long programme, which is why timecode has a drop-frame variant and why mixing 24 and 23.976 material without conforming produces sync problems that accumulate over the duration.